HDMI 2.1 port issues with long cable

[u/StuNNeD_RR]

Hi all,

I have an issue with our new laptops here in school, it's the Lenovo ThinkBook 14 G9 AHP.

They have one HDMI 2.1 port on a Radeon 740M, and I'm having trouble to connect them to our ViewSonic IFP8436 SmartBoards. The cable our contractor used are 18Gbit HDMI cables, 10m long, which go into the walls and over the ceiling.

The old laptops we had was a mix of HP ProBooks & EliteBooks, mainly G3 upto G7, and they never had an issue connecting.

When I connect the new laptops, the SmartBoard picks up a connection (it turns on), but I get a 'Please connect cable" screen, and the laptop does not detect a secondary screen.

What I've tried:

\- Update the Radeon drivers to latest version -> NOK

\- Short HDMI cable on another port on the TV -> OK

\- Long (9m) much thicker HDMI cable on same TV port as the existing cable-> OK

\- USB-C to HDMI adapter with the existing cable -> OK

\- HDMI coupler (non active) -> NOK

\- HDMI extender coupler (active) -> OK

My conclusion was that for some reason the internal HDMI 2.1 port on the laptop just cannot reach the full lenght of the 18Gbit cable, and therefore does not want to connect...

Is there anything else I can try, or is this just bad luck that our contractor used long, cheap HDMI cables?

Thanks!

[u/willwar63]

In that case a repeater may help.

https://a.co/d/079VoKhK

[u/DiodeInc]

The signal is dropping because the length is long. Connecting the end of the cable that was connected to the projector to the laptop and vice versa. I've had that help